One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the media.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the recording and reproducing density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult to quickly and accurately position the read/write head over the desired information tracks on the disk. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a voice coil motor (VCM). Referring to FIG. 1, a conventional disk drive device using VCM typically has a drive arm 104, a head gimbal assembly (HGA) 106 attached to and mounted on the drive arm 104, a stack of magnetic disks 101 suspending the HGA 106, and a spindle motor 102 for spinning the disks 101. The employed VCM is denoted by reference number 105 and is connected to the drive arm 104 for controlling the motion of the drive arm 104 and, in turn, controlling a slider 103 of the HGA 106 to position with reference to data tracks across the surface of the magnetic disk 101, thereby enabling the read/write head imbedded in the slider 103 to read data from or write data to the disk 101. Thus, the VCM 105 well performs adjustments to the position of the read/write head. However, as VCM 105 possesses limited bandwidth due to its large inertia, the position control of the read/write head with respect to the track by the VCM 105 has never presented enough accuracy, and thereby the slider 103 can not attain a quick and fine position control which accordingly affects the ability of the read/write head to read data from and write data to the disk 101.
In order to solve the problem, an additional actuator mechanism, for example a PZT micro-actuator, is introduced in the disk drive device in order to modify the displacement of the slider, thus the disk drive device forms a dual stage actuator (DSA). Referring to FIGS. 2a and 2b, the disk drive device employs a PZT micro-actuator 205 as the additional actuator and the PZT micro-actuator 205 is mounted within the HGA 106 of the disk drive device. Specifically, the HGA 106 has a suspension 207 to suspend the slider 103 thereon. The PZT micro-actuator 205 is mounted on a tongue of the suspension 207 and partially incorporates the slider 103. Multiple electrical connection balls 215 (gold ball bonding or solder ball bonding, GBB or SBB) are electrically coupled the PZT micro-actuator 205 to corresponding suspension traces 225 while multiple electrical connection balls 213 are electrically coupled the PZT micro-actuator 205 to corresponding suspension traces 223. The suspension traces 223, 225 are electrically coupled with a control system (not shown) which controls the slider 103 as well as the PZT micro-actuator 205.
Referring to FIGS. 2c and 2d, the PZT micro-actuator 205 comprises a U-shaped frame 297 which comprises two side beams 205a, 205b. The side beam 205a has a PZT element 235a and the side beam 205b has a PZT element 235b. The slider 103 is mechanically connected with the two side beams 205a, 205b of the PZT micro-actuator 205 by epoxy 212 at bonding points 206 of the slider 103. The bottom of the U-shape frame 297 is attached to the tongue of the suspension 207. The slider 103 and the frame 297 mutually form a rectangular hollow structure. The slider 103 and the side beams 205a, 205b are not directly connected to the tongue of the suspension 207 and thus enable the slider 103 and the side beams 205a, 205b to move freely with respect to the tongue of the suspension 207. Referring to FIG. 2e, when an actuating power is applied through the suspension traces 225 to the PZT micro-actuator 205, the PZT elements 235a, 235b will expand or contract, causing the beams 205a, 205b to bend in a common lateral direction. That is, when the sine voltage is input to the PZT element 235a and 235b, in the first half period, the side arm 205a will bend toward outer side 300a, while, in the second half period, the side arm 205b will bend toward outer side 300b. Thus the initial rectangular hollow structure becomes approximately a parallelogram, leading the slider 103 to undergo a lateral translation, through which successfully adjusts the slider's position. Therefore, the PZT micro-actuator 205 enables a smaller recording track width and a higher ‘tracks per inch’ (TPI) value, and thus creates a possibility of improving surface recording density.
In order to test a displacement performance of the DSA such as the displacement to identify whether the DSA has the adjustment capability, a prior art provides an AC (Alternative Current) testing method which uses the magnetic head to read and write information on the disk by a R/W tester. Referring to FIG. 3a, when writing operation is executed while the actuator is driven by sine voltage, a non-circular track 302 will be recorded on the disk 101. The R/W tester can do scanning of read-out information along the disk-rotating direction in the track of the disk 101 at each of off-track directions. The read-out information or output amp(xm, yn) is two-dimensional, wherein xm denotes a certain off-track position and yn denotes a certain disk-rotating position. Referring to FIG. 3b, at a given disk-rotating position y1, the read-out information amp(xm, y1) at the off-track position xm is the maximum. FIG. 3c shows three response curves 501′, 502′, 503′ respectively indicating output amplitude at given disk-rotating positions 501, 502, 503. By plotting these off-track positions where the read-out information become maximum at the disk-rotating positions y1, y2, y3 . . . yn and by connecting these plotted points, a displacement curve 150 on the magnetic disk can be obtained which indicates a center line of the magnetic information. As seen from FIG. 3c, the curve 150 is a plot of maximum output amplitude at point 505, 506, 507 of the three response curves 501′, 502′, 503′, The displacement curve 150 corresponds to displacement of the actuator during write operation. Thus, a response performance of the actuator in response to the applied alternating voltage is determined.
However, the test method arises various problems. According to FIG. 3b, if the amplitude of the alternating voltage is small, for example less than 5 v, it is really difficult to define the points 505, 506, 507 and thus the displacement value is difficult to judge. So the test method has measurement accuracy issue. Furthermore, referring to FIG. 3d, when the amplitude of the alternating voltage is small, it is extremely tough to seek out maximum amplitude positions 508, 509 thus hampering plotting displacement curve, thus unable to test the displacement performance of the DSA, which is another negative factor of the prior method. That is, the method has a limitation on the displacement measurement especially in a lower operation voltage. Thirdly, because of requiring the R/W tester testing two-dimensional read-out information, the prior method is complex, which unavoidably and unfavorably makes the testing time long and accordingly causes the test cost extremely high.
Hence, a need has arisen for providing an improved performance test method of an HGA to overcome the above-mentioned problems.